Time-delay network



Patented Dee. I31, 1946 'UNITED srATEs PATENT orrlcE 13.607 TnuE-DELY NETWORK Michael J. Ill Toro, Brooklyn, N. Y., assignor, by mesne assignments, to Hazeltine Research, Ino.,

Chicago, Ill., a corporation of Illlnols Application March 12, 1945, Serial No. 582.283

6 Clalms.

' known in the art and are inthe form of a balanced or unbalanced circuit. A balanced delay network of the prior art comprises a pair of similar distributed windings coaxially wound about i a common supportin'g core structure but with opposed pitches to contribute to the network uniformly dlstributed inductance and capacita'nce. The physical characteristics of the windings, such as dimensions, number of turns per unit length, andconductor size determine the total time delay of the network. The losses and imperfections ofthe windings determine theattenuation and the pass-hand characteristics of the network. While such prior art time-delay networks have proved to be operative, they are subject to certain inherent limitations which may be undesirable in particular installatlons. For example, .the arrangement is susceptible to two distinctly difierent modes of Operation: (1) balanced or normal Operation wherein the currents in corresponding portions of its windings are out oi' phase and (2) unbalanced or abnormal operation wherein the currents in corresponding-portions of its windings are in phase. Additionally, a balanced circuit is generally required for transferring signal energy to. or from the network.

An unbalanced delay network of the prior art comprises a single distrlbuted winding and an associated ground-return path. Thev ground-r'etum path is usually provided by a slottedmetal tube which also serves as a supporting core f structure for the winding. The capacitance be- `-"twee`n the winding and its core structure supplles tie distributed capacitance of the network which,

together with the mductane of the winding, determines the total time delay. A particular time delav--\may be obtained by aopropriately selecting the physical characteristics of the winding and its corefstiucture. Such an arrangement is subject to but a single mode of operation and an unbalanced circuit may be utilized for transferring energy with reference thereto. To this extent the unbalanced delay network is more desirable than the described balanced arrangement. However, such unbalanced networks of the prior art have been subject to serious loss.

problems. vFor example, the eddy-current loss in the core structure has been severe since the core is closely positioned with reference to a large portion of the surface of the winding in order to furnish thedesired distributed capacitance in the network. Additionally, it is found that the core structure undesirably shields the magnetic fleld of the winding and reduces the inductance of the network.

It is an object of the invention, therefore, to

. provide* an improved time-delay network for translating signal components included within a predetermined range of frequencies and which .avoids one or more of the above-mentioned limitations of prlor art arrangements.

It is another object of the invention to provid an improved time-delay network of the unbalanced or three-terminal type for translating with minimum attenuation slgnal components included within a predetermined range of frequencies.

It is a further object of the invention to provide an improved time-delay'network for translatng signal components included within a predetermined range of freouencies and having a relatively long time delay but reduced space'requirements.

In accordance with the invention a time-delay network for translating signal components inv cluded within a predetermined range of frequencies comprises an elongated and substan-v tially solid core structure of conductive. material. The network includes an elongated winding insulated from'but electrically coupled along its length to the core structure to provide in the network a distributed capacitance comprising the capacitance between the core structure and the winding for determining, in conjunction with the inductance of the winding, the time delay of the network. The core is constructed to have such conductivity that the eddy-current and conductiQn-Qm'rent losses thereof are approximately auaeor 3. equal at the mid-frequency of frequencies.

For a better understanding of the present invention, together withgother and further objects thereof, reference is had to the following description-1 taken in connection withthe .accompanying drawing, and its Scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a schematic represenof the aforesaid range tation of an unbalanced time-delay network in.

comprises an elongated and Substantially solid core StructureV II) of conductive material. Preferably, the material of the core Structure also is such as to provide a high permeability for a purpose to be made clear hereinafter. Where the IE for applying signals to the network is provided at one end of winding II, while an output terminai I6 for deriving delayed. signals therefrom is provided at the' opposite end of the winding.

The described arrangement will be seen to constitute an .unbalanced or three-terminal network. ,It may be considered as a' three-terminai network inasmuch as it comprises an input terminal Ili, an output terminai IBan'd'a common or ground terminal Il. In the Schem'atic circuit diagram of Fig. 2, which is approximately the electrlcal equivalent of the Fig. 1 arrangement, the distributed inductance of winding II is shown as Series-connected inductors Li, Li and the distributed capacitanee between the winding and its core Structure is designated by Shunt-connected condensers Ci, C1. This circuit arrangement in- The network is in the form of a simulated transmission line an'd cluding .Series-connected inductors and shuntconnected condensers essentially comprises `a transmisson line having a given total time delay. 'As will be made clear presently, the network isconstructed through appropriate proportioning of the conductivity of its core Structure to v have a minimum attenuation over a given pass core Structure is both conductive and magnetic, V

it may include comminuted graphite and iron particles molded into a conductive rod of any desired diameter andv length.

' The network also includes an elongated or distributed winding I I wound' around core Structure III to be mechanically supported thereby. The

winding is insulated from its supporting core Structure by means of an insulating sleeve or tape I2. although this insulation may be omitted where the insulation of the winding has sufllciently high dielectric properties. Due to the inherent capacitance between winding II and conductive core III, the winding is electrically couoled along its length to the core-Structure to provide in the delay network a distributed capacitance, namely, the capacitance between the core Structure and the winding.I This capacitance, in conjunctfon with theinductance of winding I I, determines the total time delay'of the network since the total time delay of any such4 network is proportional to the geometric mean of its total inductance and total cabacitance. The diameter, length and permeability of core Structure IU; the Sizey and type of conductor utilized in fabricating winding II, the number and pitch of the winding convolutions are selected to aiord such desired values of inductance and capacitance that the network produces a certain total time delay. In this connection, it will be appreciated that an increase in the diameter or length of the core Structure and winding results in higher values of inductance and capacitance, while increasing the number of turnS per unit length of the winding increases primarily only the inductance. Likewise, the inductance alone may be increased to a desired value by proportioning the core Structure for higher permeability. v

The time-delay network' further includes a connector I3, having a substantially lower im- Dedance than the core Structure and connected thereto adjacent'one end of winding II, for provding a -low-impedance path to a common terminal, usually ground, from the core Structure. The common or ground terminai iS designated Il and the connection I3 thereto may comprise a Silver-plated conductive Strap; An input terminal band for translating signal components included within a predetermined range of frequencies. By vi rtue of this feature, signal components included within a desired frequency range and applied to input terminal IS are translated with minimum attenuation and distortion to output terminai IS. i

- conduction-current losses" as herein -used designates the losses resulting from current flow within the network as distinguished from losses attributable to induced currents, induced by actual vcurent flow within the network. The eddy-current losses which do result from induced currents are associated with the inductance of winding II. .These losses may be considered as occurring in the resistors Re, Re shown in shunt relation with the Series-connected inductors Li, L1. The conduction-current losses on the other hand are associated with the currents flowing through these inductors and the return path to ground and may be considered to' occur'in the resistors Re, Re of Fig. 2. Since the magnitudes of both the eddy currents and the conduction currents are determined, at least in part, by the conductivity of core StructureV II), the core conductivity is eifective to determine the attenuation characteristic of the network and has a critical value for minimum attenuation. The' optimum conductivity of the core, required for attaining minimum attenuation and maximum Q of the network, may be determined with the aid of the following expressions in which:

winding il ,ieffective series resistance per unit length of network of conduction-current and eddy-current loss resistances (ohms per meter).

-=21r times the operating frequency.

wm=21r times the mid-frequency of the pass hand of the network.

to which it is ailxed.

For the assumed conditions From Equations 1 and 5 it is seen that` the attenuation caused by the conduction-current losses in Re is independent of `frequency while that attributableto the eddy-current losses in R" varies directly as the square of the frequency. i

A1so,`it is to beinoted that attenuation factors Rs and R. vary in opposite senses with variations in the core resistivit'y p. Thus, the total attenuation Rs may be minimized by selecting a value of core resistivity which causes the factors Bc and R to be equal at the mid-frequency of the pass band of the network. Where this condition is establishedz,

indicates the preferred value of the factor 6 at least one and, preferably, a plurality of longitudinally or axially extending slots 20,' 20. Such a core structure is obtainable'by molding the core about radially disposed ldielectric strips. The dielectric strips have a very small cross section as compared with that of the coreV I0 so that while the core includes longitudinal slots the slots are' sufnciently small in cross section that the core may nevertheless be considered as substantially solid. The presence of the longitudinal slots modifies the eddy-current paths of the delay network by precluding a complete circumferential path around the periphery of the core. This arrangement still further reduces the total attenuation of the network and increases. its Q in the manner described in the above-identifled copending application Serial No. 582,285.

In Fig..l 4 there is represented a further embodiment of the delay network of Fig. 1, the instant modification including a longitudinal nonmagnetic conductor 30, conductively connected along its length to core structure I0 and connected by way of connector I3 to the common or ground terminai M. More specifically, conductor 30 is embedded within the core so as to be conductively connected therewith and extends beyond each end of the core structure. Its projecting ends may be threaded, as illustrated, to facilitate securing the delay network to a supporting structure. Conductor 30 is selected to have a substantially lower impedance per unit length than that of core I0 and such a small cross-sectional configuration as compared with that of the core as to .be linked by only'a small fractional portion' of the magnetic flux of winding l I. The conductor 30 may comprise a length of. copper rod and has such a smallradius in comparison with the radius of the core'structure that the core may be considered'as substantially homogeneous.

The schematic circuit diagram of Fig. 5is the approximate electrical' bequival'ent of thevdelay i network of Fig. 4 and is generally similar to the schematic circuit diagramv of- Fig. 2', corresponding components thereof beingl designated' by the same reference characters.

In determining the conductivity of` core structure I0 of the Fig. 4 embodiment required to obtain minimum attenuation and maximum Q, it will again be assumed that the resistance of winding I I is negligible' It will be further assumed that a single grounding conductive strap 3,0 is included in the core structure having an i-mpedance per unit length which is also negligible. For the assumed conditions, conductor 30 of' Fig. 5 may be construed' as a ground plane associated with the network so that the conduc- 4 tion-current loss resistors Re are inserted in. the

sired inductance per turn or total inductance of i winding il and having computed from Equation 8 the core resistivity for minimum attenuation, the percentage of conductive material to be in- V cluded in the core structure may be readily determine'd for a core of a given length and given diameter. When the core is constructed in this manner its conductivity is such that the eddy- `*\current losses and the conduction-current losses shunt arms of the network. In deriving the expressions for the construction of the network to obtain minimum attenuation and maximum Q, the following symbols in addition to those identii fied above are used:

The Fig. 3 embodiment of the invention is genao=radius of conductor 30 (meters).

Ci=distributed capacitance per unit length of the network (farads per meter).

Ri =characteristic impedance of delay network (ohms).

Rp=total radial resistance of core structure III (ohms).

ln=natural logarithm.

tg=one-way delay of network (seconds).

lttii=one--way delay of network per unit length (seconds). f

saraso? 1=phase shift of network per turn of winding Where, as in the assumed embodiment of the core Structure, a single conductivegrounding From Equation 14 it is noted that in' the network of Fig. 5 the attenuation per unit length caused by the conduction-current losses in Re and the eddy-current losses in R" both vary directly as thesquare of the frequencybut Vary in opposite senses with core resistivity' p. The total attenuation per unit length caused by R. may, therefore, be minimized by selecting the value of core resistivity which causes the atmuation factors Re and R" to be equal. Where the core Structure is so selected:

Equation 16 is an expression for-the resistivity of core Structure I of the network, resulting in minimum attenuation and maximum Q of the' network. The factors of this equation are deflnitely known for a given network construction So that the' particular core construction necessary for minimum attenuation for arrangementsof the type illustrated in Fig. 4 may be readily determined. In this construction; as shown by Equation 16, the core resistivity is independent of frequency. Hence, the optimum core resistivity causes the eddy-current losses in the core structure to be equal to the conduction-current losses thereof at all frequencies within Vthe pass hand of the network. y

As described above,- conductor 30 has a very small cross section ascompared with that of core structure N. For this reason the conductor occupies but a small fractional portion of the magnetic field established by winding H and therefore is linked by only a small fractional portion of. the magnetic flux of the winding. While a single conductor is illustrated in" the core structure of the 4.embodiment, a plurality of similar low-impedance conductors may be provided if desired. The'advantage of increasing the number of such conductors is pointed outin related copending application Serial No. 582,284. While both experience and theory show'that best results are Vobtained when the eddy-current and conduction-current losses of the time-delay networks are equal at the mid-frequency of the pass band, the advantages of the invention may nevertheless be obtained to a substantial degree if these losses are approximately equal. The term approximately equal as used in the description and appended claims is intended to mean that one of the losses may be between 1.0 and 0.1 the other. Where the attenuation factors are proportioned within the limits of this deiinition, the ratio of the actual Q of the network to the maximum Q, obtained when the eddy-current and conduotion-current losses are equal, is greater than 0.57.

Terminals M, i5 and II permit the delay networklto be coupled as desired in Signal-translating systems. Such a network is subject to a wide variety of applications and may be utilized, for example, to obtain a desired time delay of applied transient signala. Also through appropriate termination of the output circuit of the network, echoes or reflections of applied signals may be obtained, as with well-known reflecting transmission-line arrangements. Additionally, such a network is useful in pulse-generating systems wheren similar time-delay netw'orks determine the duration and spacing of the generated puises.

Each of the described arrangement's has' the advantags of an unbalanced or three-terminai network and minimum attenuation to applied signais within .a desired range ofzfrequencies. Furthermore, as pointed out above, by appropriate selection of the permeability of core structure N, the delay network may exhibit a very high inductance and, cons'equently, produce'unusually long time delays for a network Structure 45 of given physical dimensions.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modiflcations as fall within the true. spirit and scope of the invention.

what is'claimea is:

1. A time-delay network for translating signal components included withinl a predetermined range of frequencies ,comprising,- an elongated and substantialiy solid core Structure of conductive material, an elongated winding insulated from but eiectrically coupled along its length to said core Structure to provide in said network a distributed'capacitance comprising the capaci-l tancebetween said-winding and said core structure for determining in conjunction with the inat the mid-frequency of said range.

2. A time-delay network for translating signal components included within a predetermined range of frequencies comprising, a'n elongateci and substantially solid core Structure of conduc- 76 tive and magnetic material, an elong'ated wind- 9 ing insulated from but electrically coupledalon its length to said core Structure to provide in said network a, distributed capacitance comprising the capacitance between said winding and said core Structure for determining in coniunction with the inductance of said winding the time delay of V said network, said core Structure having such conductivity that the eddy-current and conduction-current losses thereof are approximately equal at the mid-frcquency of said range and having such permeability that said winding ,has a predetermned inductance per turn.

3. A time-delay network for translating signal components included within a predetermined range of frequencies comprising, an elongated and substantially solid core Structure of conductive material having at least one longitudinally extending slot, an elongated winding insulated from but electrical-ly coupledv along its length to said core Structure to provide in said network a distributed capacitance comprising the capacitance between said winding and said core Strucapproximately equal at all frequencies within said range.

5. A time-delay network for translating signal components included within a predetermined range of frequencies comprising, an eiongated and Substantially solid core Structure of conductive material, an elongated winding insulated from but electrically coupled along its length to ture. for determining in conjunction with the inductance of `said winding the time delay of said network, said core Structure having such conductivity that the' eddy-current and conduction-current losses thereof are approximately equal at the mid-frequency of said range.

4. A time-delay network for translating signal components included within a predetermined range of frequencies comprising, an elongated and substantially Solid core Structure of conductive material, an elongated winding insulated from but electrically coupled along its length to said core Structure to provide in said network a distributed capacitance comprising the capacitance between said winding and said core Structure for determining in conjunction with the inductance of said winding the time delay of said network, and a longitudinal conductor conductively connected along itslength to said core Structure and having a Substantially lower impedance per unit length than said core Structure and such cross-sectional conflguration as to be iinked by only a small fractional portion of the magnetic fiux of said winding, said core structure having such conductivity that the eddycurrent and conduction-current losses thereof are -said core Structure to provide in said network a distributed capacitance comprising the capacitance between said winding and said corestructure for determining in conjunction with the inductance ,of said winding the time delay of said network, and a longitudinal conductor embedded in' said core Structure lso as to be conductively connected thereto along itslength and having va substantially lower impedance per unit length than said core Structure and such cross-sectional Configuration as to be linked by only a Small fractional portion of the magnetic fiux of said `winding. said core Structure having such con- .ductivity that the eddy-current and conductioncurrent losses thereof are approximately equal at tively connected thereto along its length and extending beyond the ends of said core Structure,

said conductor having a substantially lower impedance per unit length than said core structure and'such cross-sectional configuration as to be -linked by only a Small fractional portion of the magnetic flux of said winding, and said core Structure having such lconductivity that the eddycurrent. and conduction-current losses thereof are approximately equal at all frequencies within said range.

MICHAEL J. DI TORO. 

